With recent increased use of vehicles such as hybrid cars and electric vehicles, there is increasing demand for terminals that conduct a large current, such as terminals attached to electric wires for supplying power to motors and the like. Contacts of this sort of terminal are typically plated with Ag (silver) whose contact electrical resistance is low. When terminals are fitted to each other, Ag layers on respective contacts come into contact with each other, and the terminals are electrically connected to other.
However, since Ag is a relatively soft metal and is likely to cause adhesion, a terminal pair in which Ag layers are exposed on the surfaces of contacts is likely to be worn due to Ag adhesion. In particular, if the Ag layers slide over each other during terminal insertion or the like, wearing due to adhesion becomes apparent. If severe wearing appears, a base material whose contact electrical resistance is larger than that of an Ag layer is exposed and comes into contact with the corresponding terminal, and thus the connection reliability of the terminal pair becomes poor.
The present inventors conducted an in-depth study in order to address this problem, and developed a technique for sequentially layering a base plating made of nickel or copper, a silver-tin alloy layer, and a silver coating layer, on a base material (Patent Document 1 JP2013-231228A). In the plated member of Patent Document 1, a silver-tin alloy layer that is harder than silver is formed under a silver coating layer that is exposed on the surface, and thus the coefficient of friction during terminal insertion or the like can be lowered. As a result, the wear resistance can be improved.